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Phytophthora infestans Isolates Lacking Class I ipiO Variants Are Virulent on Rpi-blb1 Potato

December 2009 , Volume 22 , Number  12
Pages  1,535 - 1,545

Nicolas Champouret,1 Klaas Bouwmeester,2 Hendrik Rietman,1 Theo van der Lee,3 Chris Maliepaard,1 Anika Heupink,1 Peter J. I. van de Vondervoort,2 Evert Jacobsen,1 Richard G. F. Visser,1 Edwin A. G. van der Vossen,1 Francine Govers,2 and Vivianne G. A. A. Vleeshouwers1

1Wageningen UR Plant Breeding, P.O. Box 386, 6700 AJ, Wageningen, The Netherlands; 2Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, The Netherlands; 3Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands

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Accepted 15 July 2009.

A strategy to control the devastating late blight disease is providing potato cultivars with genes that are effective in resistance to a broad spectrum of Phytophthora infestans isolates. Thus far, most late blight resistance (R) genes that were introgressed in potato were quickly defeated. In contrast, the Rpi-blb1 gene originating from Solanum bulbocastanum has performed as an exclusive broad-spectrum R gene for many years. Recently, the RXLR effector family ipiO was identified to contain Avr-blb1. Monitoring the genetic diversity of the ipiO family in a large set of isolates of P. infestans and related species resulted in 16 ipiO variants in three distinct classes. Class I and class II but not class III ipiO variants induce cell death when coinfiltrated with Rpi-blb1 in Nicotiana benthamiana. Class I is highly diverse and is represented in all analyzed P. infestans isolates except two Mexican P. infestans isolates, and these were found virulent on Rpi-blb1 plants. In its C-terminal domain, IPI-O contains a W motif that is essential for triggering Rpi-blb1--mediated cell death and is under positive selection. This study shows that profiling the variation of Avr-blb1 within a P. infestans population is instrumental for predicting the effectiveness of Rpi-blb1--mediated resistance in potato.

© 2009 The American Phytopathological Society